I have a 1989 GT I'm trying to get running so I can sell, but it has me pretty baffled. It has a new alternator, a new battery, and continuity between the battery/alternator/ground. However, the alternator is simply not charging the battery, or somewhere I have a drain so huge that the alternator can't keep up. I can charge the battery up with the charger, and it starts just fine, even though the battery is only at 10.9 volts or so. Let it idle for a few minutes and it slowly drops down to 10.8, 10.7, 10.6 etc till it dies. Anyone dealt with this before?

I'm going to get the alternator tested to determine if it's a bad new one, but it was replaced because of this problem, so I kinda doubt it's the culprit.